Question 1

What gutter profile should I choose?

Accepted Answer

Half-round is the most common and cheapest profile — suitable for most domestic properties. Square-line has higher flow capacity for the same width and a more modern appearance. Ogee has a decorative moulded front and suits period properties. Deep-flow (high-capacity) is essential for large roof areas or steep pitches. The choice is partly aesthetic and partly functional based on your roof area and rainfall intensity.

Question 2

How do I calculate what gutter size I need?

Accepted Answer

The gutter must handle the peak rainwater flow from your roof. Effective roof area = plan area x pitch factor (1.0 for flat, up to 1.4 for steep). For the UK, design rainfall intensity is typically 75 mm/hour. Multiply effective area (m²) by 0.0208 litres/second per m² to get the required flow rate. Then choose a gutter profile with adequate flow capacity. For a typical semi-detached house (50-60 m² roof per side), 112 mm half-round is usually sufficient.

Question 3

What spacing for gutter brackets?

Accepted Answer

PVC gutter brackets should be spaced at maximum 1 m centres, with additional brackets within 150 mm of each union, angle or stop end. Aluminium guttering is fixed at 915 mm-1 m centres (Marley Alutec installation guides) and cast iron at 900 mm maximum centres (Hargreaves Foundry fixing instructions): despite the rigidity of the material, its weight plus standing water limits the spacing. Running outlets and stop ends should always have a bracket immediately adjacent for support.

Question 4

What fall does a gutter need?

Accepted Answer

Gutters should be installed with a fall of approximately 1:350 (about 3 mm per metre) toward the downpipe outlet. This is shallow enough to be virtually invisible but sufficient to ensure water flows to the outlet. For long gutter runs, the fall can be split by placing the outlet in the centre with falls from each end.

Profile	Width (mm)	Flow Capacity (l/s)	Downpipe Size (mm)	Max Roof Area (m²)
Mini half-round	75	~0.4	50	~17
Half-round	112	~0.9	68	~40
Square-line	114	~1.2	65 (square)	~55
Ogee	115	~1.0	68	~46
Deep-flow (half-round)	115	~1.5	68	~68
Industrial/deep-flow	170	~2.8	110	~130

Type	Size (mm)	Compatible Gutters
Round	50	Mini half-round (75 mm)
Round	68	112 mm half-round, ogee, deep-flow
Square	65	Square-line (114 mm)
Round	110	Industrial / 170 mm gutters

Material	Typical Lifespan (years)	Bracket Spacing	Notes
PVC (uPVC)	15–25	Max 1 m	Cheapest, most common, colours fade
Aluminium	30–50	915 mm–1 m	Lightweight, durable, powder-coated
Cast iron	50–100+	Max 900 mm	Heritage, heavy, needs repainting
Zinc / copper	50–80	Max 1 m	Premium, patinas naturally, bespoke

UK Guttering Profiles & Flow Rates

Common Gutter Profiles

Downpipe Sizes

Material Options

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